Gram negative infections are a major cause of morbidity and mortality especially in hospitalized and immunocompromised patients. [Duma, R. J., Am. J. of Med., 78 (Suppl. 6A): 154-164 (1985); and Kreger B. E., D. E. Craven and W. R. McCabe, Am. J. Med., 68: 344-355 (1980)]
Although available antibiotics are effective in containing the infection, they do nothing to neutralize the pathophysical effects associated with lipopolysaccharide (LPS). LPS, or endotoxin, is a major component of the outer membrane of gram negative bacteria and is releasaed when the organisms are lysed. [Ahenep, J. L. and K. A. Morgan, J. Infect. Dis., 150 (3): 380-388 (1984)]
LPS released during antibiotic therapy is a potent stimulator of the inflammatory response. Many detrimental effects of LPS in vivo result from soluble mediators released by inflammatory cells. [Morrison D. C. and R. J. Ulevich, Am. J. Pathol., 93 (2): 527-617 (1978)] LPS induces the release of mediators by host inflammatory cells which may ultimately result in disseminated intravascular coagulation (DIC), adult respiratory distress syndrome (ARDS), renal failure, and irreversible shock.
Monocytes and neutrophilic granulocytes play a key role in host defense against bacterial infections and also participate in the pathology of endotoxemia. These cells ingest and kill microorganisms intracellularly and also respond to LPS in vivo and in vitro by releasing soluble proteins with microbicidal, proteolytic, opsonic, pyrogenic, complement activating and tissue damaging effects. Tumor necrosis factor (TNF), a cytokine released by LPS stimulated monocytes mimics some of the toxic effects of LPS in vivo. Injecting animals with TNF causes fever, shock and alterations in glucose metabolism. TNF is also a potent stimulator of neutrophils.
Soluble LPS causes decreased neutrophil chemotaxis, increased adhesiveness, elevated hexose monophosphate shunt activity and O.sub.2 radical production, upregulation of surface receptors for complement, and release of granule proteins into the surrounding medium. [Morrison and Ulevich (1978)]
Both specific and azurophil compartments degranulate in response to LPS. [Bannatyne, R. M., N. M. Harnett, K. Y. Lee and W. D. Rigger, J. Infect. Dis., 156 (4): 469-474 (1977)] Azurophil proteins released in response to LPS may be both harmful and beneficial to the host. Neutrophil elastase causes degradation of protease inhibitors responsible for suppressing the coagulation cascade. This results in coagulopathies such as disseminated intravascular coagulation, a potentially lethal consequence of endotoxemia. Azurophil granules also contain bactericidal molecules such as myeloperoxidase and BPI.
Rabbit BPI was first discovered in 1975. [Weiss, J., R. C. Franson, S. Becherdite, K. Schmeidler, and P. Elsbach, J. Clin. Invest., 55:33 (1975)] BPI was isolated from human neutrophils in 1978. [Weiss, J., P. Elsbach, I. Olson and H. Odeberg, J. Biol. Chem, 253 (8): 2664-2672 (1978)].
In 1989 a 57 kD protein with similar properties was isolated from human neutrophils. [Shafer, W. M., C. E. Martin and J. K. Spitznagel, Infect. Immun., 45:29 (1984)] This protein is identical to BPI by N-Terminal sequence amino acid composition, molecular weight and source. Although, the authors were unable to reproduce the chromatographic isolation procedure used by Elsbach, et al. and Weiss, et al.
Human BPI is a 57 kD protein which binds to the outer membrane of susceptible gram negative bacteria. [Weiss, et al. (1978)] The fact that BPI is a Lipid A binding protein is evidenced by: (1) rough strains of bacteria are more sensitive to both bactericidal and permeability increasing activities of BPI [Weiss, J., M. Hutzler and L. Kao, Infect. Immun., 51:594 (1986)]; (2) mutations in Lipid A caused decreased binding and increase resistance to bactericidal activity of both polymyxin B and BPI [Farley, M. M., W. M. Shafer and J. K. Spitznagel, Infect. Immun., 56:1589 (1988)]; (3) BPI competes with polymyxin B for binding to S. typhimurium [Farley 1988]; (4) BPI has sequence homology and immunocrossreactivity to another LPS binding protein Lipopolysaccharide Binding Protein (LBP). LBP-LPS complexes have been shown to stimulate the oxidative burst on neutrophils in response to formulated peptides. High density lipoprotein (HDL), another LPS binding protein, found in human serum in complex with LPS does not show the stimulatory effect on neutrophils. BPI binding disrupts LPS structure, alters microbial permeability to small hydrophobic molecules and causes cell death (Weiss, et al., 1978). BPI kills bacteria under physiologic conditions of pH and ionic strength in vitro indicating that it may be active in vivo outside the low pH environment of the phagolysosome. All of the bactericidal and permeability increasing activities of BPI are present in the N-terminal 25 kD fragment of the protein. [Ooi, C. E., J. Weiss, P. Elsbach, B. Frangione, and B. Marrion, J. Biol. Chem., 262: 14891 (1987)] Prior to the subject invention, however, it has been understood that the beneficial effects of BPI are limited to its bactericidal effects.
Despite improvements in antibiotic therapy, morbidity and mortality associated with endotoxemia remains high. Antibiotics alone are not effective in neutralizing the toxic effects of LPS. Therefore, the need arises for an adjunct therapy with direct LPS neutralizing activity. Current methods for treatment of endotoxemia use antibiotics and supportive care. Most available adjunct therapies treat symptoms of endotoxic shock such as low blood pressure and fever but do not inactivate endotoxin. Other therapies inhibit inflammatory host responses to LPS. As indicated below, present therapies have major limitations due to toxicity, immunogenicity, or irreproducible efficacy between animal models and human trials.
Polymyxin B is a basic polypeptide antibiotic which has been shown to bind to, and structurally disrupt, the most toxic and biologically active component of endotoxin, Lipid A. Polymyxin B has been shown to inhibit LPS activation of neutrophil granule release in vitro and is an effective treatment for gram negative sepsis in humans. However, because of its systemic toxicity, this drug has limited use except as a topical agent.
Combination therapy using antibiotics and high doses of methylprednisolone sodium succinate (MPSS) has been shown to prevent death in an experimental model of gram negative sepsis using dogs. Another study using MPSS with antibiotics in a multicenter, double blind, placebo-controlled, clinical study in 223 patients with clinical signs of systemic sepsis concluded that mortality was not significantly different between the treatment and placebo groups. Further, the investigators found that resolution of secondary infection within 14 days was significantly higher in the placebo group.
A relatively new approach to treatment of endotoxemia is passive immunization with endotoxin neutralizing antibodies. Hyperimmune human immunoglobulin against E. coli J5 has been shown to reduce mortality in patients with gram negative bacteremia and shock by 50%. Other groups have shown promising results in animal models using mouse, chimeric, and human monoclonal antibodies. Although monoclonal antibodies have advantages over hyperimmune sera, e.g. more consistent drug potency and decreased transmission of human pathogens, there are still many problems associated with administering immunoglobulin to neutralize LPS. Host responses to the immunoglobulins themselves can result in hypersensitivity. Tissue damage following complement activation and deposition of immune complexes is another concern in the use of therapies involving anti-endotoxin antibodies in septic patients. Also, immunoglobulins are large molecules, especially the pentameric IgMs currently in clinical trials, and are rapidly cleared by the reticuloendothelial system, diminishing the half-life of the drug.
Endotoxins elicit responses which are beneficial as well as damaging to the host. Endotoxemia induces production of LPS binding proteins from the liver and causes release of microbicidal proteins from leukocytes. In applicants' studies of neutrophil proteins involved in host defense, it has been determined that one of these proteins, BPI, is not only a potent microbicidal agent in vitro, but it also interferes with the ability of LPS to stimulate neutrophils. Specifically, it has been demonstrated that BPI binds to solve LPS and neutralizes its ability to activate neutrophils. Accordingly, this invention provides a therapeutic method for the treatment of LPS toxicity in gram negative septicemia.